Where the atria meet the ventricles, there is an area of special cells - called the atrio-ventricular node - which pass the electrical signals throughout your heart muscle by a system of electrical pathways, known as the conducting system. Blood is pumped through the valves into the ventricles. This signal crosses the atria, making them contract. The electrical signal starts in the right atrium where your heart’s natural pacemaker - the sino–atrial node - is situated.
Your blood is pumped around your body through a network of blood vessels:įor your heart to keep pumping regularly, it needs electrical signals which are sent to the heart muscle telling it when to contract and relax. The blood then returns to the left side of the heart, ready to be pumped back out to the brain and the rest of your body. It pumps this to your lungs, where it picks up a fresh supply of oxygen. The right side of the heart receives blood that is low in oxygen because most has been used up by the brain and body. Your heart, blood and blood vessels together make up your cardiovascular system (or heart and circulatory system). Your heart pumps blood around the body all the time - about five litres (eight pints) of it - and this is called circulation. These left and right sides of the heart are separated by a wall of muscle called the septum.
The two larger lower chambers are the ventricles. The two small upper chambers are the atria. There are four chambers that make up the heart – two on the left side and two on the right.
These layers are surrounded by the pericardium, a thin outer lining protecting your heart.
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